Rupture disk assembly

ABSTRACT

An improved rupture disk assembly and methods and apparatuses for forming a rupture disk are disclosed. The rupture disk assembly includes a rupture disk having a flange connected to a dome-shaped rupturable portion by a transition area. The rupturable portion includes a structural apex formation at or near the apex of the dome and is configured to rupture when exposed to a fluid having a predetermined pressure. Preferably, a safety member is disposed adjacent the rupture disk. The safety member includes a hinge about which the disk bends when the disk ruptures. The present invention is also directed to an apparatus and method for consistently, accurately, and repeatably forming a structural apex formation in a rupture disk before the formation of to the rupture disk dome, during the formation of the rupture disk dome, and after the formation of the rupture disk dome.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 09/310,848, filed on May 13, 1999 for Rupture Disk Assembly.

BACKGROUND OF THE INVENTION

[0002] This invention relates to pressure relief systems. Moreparticularly, the present invention relates to an improved rupture diskassembly for a pressure relief system and to apparatuses and methods forforming and manufacturing rupture disks.

[0003] Pressure relief assemblies are commonly used as safety devices insystems containing pressurized fluids in gas or liquid form. A pressurerelief assembly will vent fluid from the system when the pressure in thesystem reaches an unsafe level. A number of emergency conditions,including fire and system failure, can create dangerous pressure levels,which require immediate relief to preserve the safety of the system.

[0004] Generally, a pressure relief assembly includes a rupture diskthat is sealed between a pair of support members, or safety heads. Thepressure relief assembly is then typically clamped, or otherwisesealingly disposed, between a pair of conventional pipe flanges in thepressurized system. One of the pipes conducts pressurized fluid to oneside of the pressure relief assembly and the other pipe provides anoutlet to a safety reservoir or may be open to the environment. Thesupport members include a central opening that exposes a portion of therupture disk to the pressurized fluid in the system. The exposed portionof the rupture disk will rupture when the pressure of the fluid reachesa predetermined differential pressure between the inlet and outletsides. The ruptured disk creates a vent path that allows fluid to escapethrough the outlet to reduce the pressure in the system.

[0005] Rupture disks typically have a dome shape and can be eitherforward acting or reverse acting. In a forward acting disk, the concaveside of the dome faces the pressurized fluid, placing the material ofthe disk under tension. In a reverse acting disk, the convex side of thedome faces the pressurized fluid, placing the material of the disk undercompression. In the reverse acting disk (also known as a reversebuckling disk), when the pressure of the fluid exceeds the predeterminedlevel and the material of the disk structure cannot withstand thepressure, the dome of the disk will buckle and begin to reverse. Thisreversal, or buckling, will begin at a particular point on the disk,known as the point of initial reversal. As the disk continues toreverse, the material of the disk is torn by an opening means to createthe vent path to release the pressurized fluid.

[0006] Both types of disks commonly include score lines (areas ofweakness) to facilitate the opening of the disk. In a reverse bucklingdisk, the disk will tear along the score line when the disk isreversing. Selected portions of the disk are usually left unscored,acting as a hinge area, to prevent the disk from fragmenting uponbursting and escaping along with the pressurized fluid. Additionally,pressure relief assemblies are known that include safety members toassist in opening the disk and to absorb the energy created by thebursting of the disk to attempt to prevent the disk from fragmenting.

[0007] In an emergency situation, where the system pressure becomesunsafe, it is important to reduce the pressure as quickly as possible.The American Society of Mechanical Engineers (ASME) code establishesminimum performance requirements for fluid flow rates through pressurerelief systems. The size and shape of the opening created when the diskbursts is a limiting factor on the rate at which fluid can escape thesystem. A burst disk having a large, unobstructed opening will performbetter than a burst disk having a small, obstructed opening because thevelocity head loss (i.e. pressure drop) over the large, unobstructedopening will be lower than the velocity head loss over a smaller orobstructed opening. The lower velocity head loss translates to a lowerflow resistance (K_(r)) and, thus, a greater flow rate through the disk.

[0008] Adjusting different facets of the disk design, including the sizeof the rupturable portion of the disk and the location of the scoreline, can control the size and shape of the opening created when thedisk bursts. A larger disk has the potential to create a larger opening.

[0009] Another factor affecting flow resistance is the nature of thefluid in the pressurized system. It has been found that rupture disksopen differently depending on the nature of the fluid in the system.Typically, a disk burst in a gas environment will open more fully than adisk burst in a liquid environment. Thus, to meet desirable flowresistance performance requirements, the design of a disk may have to bedifferent if the disk is being used in a liquid application, even if theliquid is at the same pressure as a similar gas application.

[0010] An additional factor of disk design that affects flow resistanceis the thickness of the rupturable portion of the disk. A disk made of athinner material will bend easier than a disk made of a thickermaterial. Thus, for disks rupturing at the same fluid pressure, athinner disk is more likely to completely open and create a large,unobstructed opening than a corresponding thicker disk.

[0011] However, a disk made of a thinner material is more susceptible todamage than a thicker disk. Any damage to the rupture disk could alterthe actual burst pressure of the disk. This is particularly an issue inlow pressure, reverse buckling disks where the disk material must bethin to burst at the desired low pressure. The thinner, low pressuredisks are more likely to be damaged during installation, which maycompromise the structural integrity of the disk and cause the disk toreverse at a pressure significantly less than the desired rupturepressure. In these situations, the material of the disk does not tear asexpected and the disk may completely reverse without tearing. Thereverse buckling disk then acts like a forward acting disk and the fluidpressure places the material of the disk in tension. Because the tensilestrength of the disk material is greater than the correspondingcompressive strength, the disk may not tear to create the vent pathuntil the pressure of the system significantly exceeds the desiredrupture pressure. This over-pressure condition could result in damage tothe system that the rupture disk was intended to prevent.

[0012] Rupture disks are rated by their performance in a damagedcondition. This rating is generally known as the damage safety ratio ofthe disk and is determined by dividing the actual pressure at which adamaged disk ruptures by the desired, or rated, rupture pressure of thedisk. A damaged disk with a damage safety ratio of 1 or less will burstat the desired rupture pressure, or before the pressurized fluid reachesthe desired pressure, thereby preventing any damage to the system.

[0013] Another important performance rating of a rupture disk is theburst accuracy of the disk. There are variations in materials,manufacturing, and installation that may result in any given two disksin a manufacturing lot of seemingly identical disks not bursting at thesame pressures. Thus, there is typically a variation in actual burstpressure among disks having the same rated pressure. With currentrupture disk design and manufacturing methods, rupture disks willtypically burst at a pressure that is less than 5% of the rated pressureor less than 2 psig when the rated pressure is below 40 psig. Thus, toprevent premature disk rupture and to provide a safety margin, thestandard operating pressure of a system should not exceed 90% of therated pressure of a rupture disk used in the system.

[0014] In light of the foregoing, there is a need for a pressure reliefassembly that provides a low flow resistance K_(r) in both liquid andgas applications. There is further a need for rupture disks that have anaccurate and repeatable burst pressure and thus can be used in a highoperating capacity. There is still further a need for a rupture diskhaving a low damage safety ratio so that an inadvertently damagedreverse buckling disk does not create a potentially dangerousover-pressure situation in either liquid or gas applications.

SUMMARY OF THE INVENTION

[0015] Accordingly, the present invention is directed to a pressurerelief assembly that obviates one or more of the limitations anddisadvantages of prior art pressure relief assemblies. The advantagesand purposes of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages and purposes of the invention will be realized and attainedby the elements and combinations particularly pointed out in theappended claims.

[0016] To attain the advantages and in accordance with the purposes ofthe invention, as embodied and broadly described herein, the inventionis directed to an apparatus for indenting a rupture disk that includesan annular flange and a rupturable portion having a domed shape. Theapparatus includes a first member and a second member. The first memberhas an opening and is configured to engage a first side of therupturable portion of the rupture disk. The second member is disposed ona second side of the rupturable portion of the rupture disk and isaligned with the opening in the first member. The second member engagesthe rupturable portion at or near the apex of the domed shape anddisplaces a section of the rupturable portion relative to the firstmember to thereby create an indentation in the rupturable portion at ornear the apex of the domed shape.

[0017] In another aspect, the present invention is directed to a methodof forming an indentation in a rupture disk that includes an annularflange and a rupturable portion having a domed shape. According to themethod, a first side of the rupturable portion is supported with a firstmember having an opening. A second member aligned with the opening inthe first member is engaged with a second side of the rupturable portionat or near the apex of the domed shape to displace a section of therupturable portion relative to the first member and thereby create anindentation at or near the apex of the rupturable portion of the rupturedisk.

[0018] In still another aspect, the present invention is directed to amethod of forming an indentation in a rupture disk. According to themethod, a first side of a rupture disk blank is supported with a firstmember having an opening. A second member aligned with the opening inthe first member is engaged with a second side of the rupture disk blankat or near the center of the rupture disk blank to displace a section ofthe rupture disk blank relative to the first member, thereby creating anindentation at or near the center of the rupture disk blank. A portionof the rupture disk blank is subject to a pressurized fluid to form saidportion of the rupture disk blank into a domed shape such that theindentation is disposed at or near the apex of the domed shape.

[0019] According to another aspect, the present invention is directed toan apparatus for forming a rupture disk from a blank. The apparatusincludes a clamp configured to fixably secure an outer perimeter of theblank. The clamp has a pathway configured to direct a pressurized fluidagainst the unclamped portion of the blank. The pressurized fluid actson the unclamped portion of the blank to displace the unclamped portionof the blank relative to the clamp. A mold having a concave shapereceives the unclamped portion of the blank as the unclamped portion isdisplaced relative to the clamp and forms the unclamped portion of theblank into a domed shape generally corresponding to the concave shape ofthe mold. A member disposed in the mold engages the unclamped portion ofthe blank as the unclamped portion is displaced relative to the clamp tothereby form an indentation at or near the apex of the domed shape.

[0020] In still another aspect, the present invention is directed to amethod of forming a rupture disk from a blank. According to the method,the outer perimeter of the blank is clamped and a pressurized fluid isdirected against a central portion of the blank. The pressurized fluiddisplaces the central portion of the blank relative to the outerperimeter and into a mold having a concave shape. The central portion ofthe blank is formed into a domed shape that generally corresponds to theconcave shape of the mold. A member is engaged with central portion ofthe blank as the central portion is formed into the domed shape to forman indentation at or near the apex of the domed shape.

[0021] According to yet another aspect, the present invention isdirected to a rupture disk assembly to be sealed in a pressurizedsystem. The assembly includes a rupture disk that is configured toreverse when exposed to a fluid having a predetermined pressure. Therupturable portion defines an opening therethrough. A liner is disposedbetween the rupture disk and the pressurized system and is configured tocover and seal the opening in the rupturable portion of the rupturedisk.

[0022] According to still another aspect, the present invention isdirected to a rupture disk to be sealingly engaged with a pressurizedsystem. The rupture disk includes an annular flange and a rupturableportion that is configured to rupture when exposed to a fluid having apredetermined pressure. The rupturable portion has a domed shape with aconvex surface and a corresponding concave surface and a structural apexformation disposed at the apex of the dome. The structural apexformation includes a crease formed in at least one of the concave andconvex surfaces.

[0023] In still another aspect, the present invention is directed to arupture disk assembly to be sealed in a pressurized system. The rupturedisk assembly includes a rupture disk having a dome-shaped rupturableportion that includes a convex surface and a corresponding concavesurface forming a dome area. The rupturable portion includes a scoreline that has a first and a second end and creates a line of weaknessalong which the rupturable portion will tear when the rupturable portionof the rupture disk is exposed to a fluid above a predeterminedpressure. A safety member is disposed adjacent the concave surface ofthe rupture disk. The safety member includes a flange and a hinge thatdefines first and second pockets configured to receive the area of therupturable portion adjacent the respective ends of the score line whenthe rupture disk ruptures.

[0024] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate one embodiment ofthe invention and together with the description, serve to explain theprinciples of the invention. In the drawings,

[0026]FIG. 1 is a cross sectional view of a pair of support members anda rupture disk according to the present invention positioned between apair of pipe flanges;

[0027]FIG. 2 is a top view of a rupture disk and a safety memberaccording to the present invention;

[0028]FIG. 3a is a cross sectional view of the rupture disk and safetymember of FIG. 2, taken along line Z-Z;

[0029]FIG. 3b is a cross sectional view of an alternative embodiment ofthe rupture disk and safety member of FIG. 2, taken along line Z-Z;

[0030]FIG. 4 is a cross sectional view of the rupture disk and safetymember of FIG. 2, taken along line Y-Y;

[0031]FIG. 5 is a cross sectional view of a pair of support members anda rupture disk according to the present invention positioned between apair of pipe flanges, illustrating the rupture disk in a burst state;

[0032]FIG. 6 is a perspective view of a rupture disk having a centralindentation according to the present invention;

[0033]FIG. 7 is a cross sectional view of the rupture disk of FIG. 6;

[0034]FIGS. 8 and 9 are top plan views of alternative embodiments ofcentral indentations according to the present invention;

[0035]FIG. 10 is a cross-sectional view of an apparatus for creating anindentation in a rupture disk in accordance with the present invention;

[0036]FIG. 11 is a cross-sectional view of another embodiment of a punchtip for creating an indentation in a rupture disk; FIGS. 12a-12 c areend views of a punch tip according to the present invention;

[0037]FIG. 13 is a cross-sectional view of another apparatus forcreating an indentation in a rupture disk in accordance with the presentinvention;

[0038]FIG. 14 is a partial cross-sectional view of the apparatus of FIG.13, illustrating the punch tip engaged with the rupturable portion ofthe rupture disk;

[0039]FIG. 15 is a top view of a rupture disk having an opening in therupturable portion in accordance with the present invention;

[0040]FIG. 16 is a side view of a rupture disk assembly include arupture disk having an opening in the rupturable portion;

[0041]FIG. 17 is a top view of another embodiment of a safety member inaccordance with the present invention;

[0042]FIG. 18 is a side view of the safety member of FIG. 17; and

[0043]FIG. 19 is a cross-sectional view of a rupture disk having anindentation formed in accordance with an aspect of the presentinvention.

DETAILED DESCRIPTION

[0044] Reference will now be made in detail to the presently preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings. Wherever possible, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts. An exemplary embodiment of a pressure relief assembly of thepresent invention is shown in FIG. 1 and is designated generally byreference number 20.

[0045] In accordance with the present invention, there is provided apressure relief assembly that includes an inlet support member thatdefines an inlet bore for conducting a pressurized fluid, an outletsupport member that defines an outlet bore for relieving the pressurizedfluid, and a rupture disk. The rupture disk has a rupturable portionincluding a convex surface and a corresponding concave surface thatdefines a dome area. The rupture disk also includes a flange for sealingengagement between the inlet and outlet support members to align theconcave surface with the outlet bore and the convex surface with theinlet bore. In the illustrated embodiments, the pressure relief assemblyis depicted as a pretorqued pressure relief assembly. It iscontemplated, however, that the present invention may also be used withnon-pretorqued pressure relief assemblies or as a component of a weldedassembly.

[0046] As embodied herein and as illustrated in FIG. 1, pressure reliefassembly 20 includes an inlet support member 30 and an outlet supportmember 32. Inlet support member 30 defines an inlet bore 34 and has aseries of internally threaded bolt holes 43 (only one of which isillustrated in FIG. 1) surrounding the inlet bore. Outlet support member32 defines an outlet bore 36 and has a series of bolt holes 41 (only oneof which is illustrated in FIG. 1) that correspond to bolt holes 43 ofinlet support member 30. It is contemplated that the inlet and outletsupport members may be safety heads, pipe flanges, or any combination ofstructures capable of sealingly engaging the rupture disk with apressurized system.

[0047] As also shown in FIG. 1, a rupture disk 44 is positioned betweeninlet support member 30 and outlet support member 32. Rupture disk 44includes a flange 48 and a rupturable portion 45. Flange 48 is connectedto rupturable portion 45 by transition area 49. It is contemplated thatthe rupture disk and safety member of the present invention can also beutilized in sanitary environments, wherein well-known sanitary fittingswill be utilized to engage the rupture disk.

[0048] Rupturable portion 45 has a dome shape that includes a concavesurface 46 and a convex surface 47 that define a dome area designatedgenerally as 35. When flange 48 is engaged with inlet and outlet supportmembers 30 and 32, rupturable portion 45 aligns with inlet bore 34 andoutlet bore 36. In a preferred embodiment, convex surface 47 extendsinto inlet bore 34 and concave surface faces outlet bore 36. It iscontemplated, however, that aspects of the present invention may beutilized in forward acting disks where the convex surface extends intothe outlet bore.

[0049] As illustrated in FIG. 2, rupturable portion 45 includes a scoreline 80 that has a first end 84 and a second end 86. Preferably, scoreline 80 transcribes an arc of approximately 300° in the concave surfaceof the dome-shaped rupturable portion. The present invention can beutilized with score lines of various configurations, such as, forexample, an intermittent score line where the score generallytranscribes an arc, but includes a series of gaps of unscored material.The score line may also completely circumscribe the rupturable portionof the disk, but include a section where the depth of the score line isshallower than the remainder of the score line. For purposes of thepresent invention, the points at which the depth of the score linechanges would be considered to be the first and second ends of the scoreline.

[0050] As described in greater detail below, score line 80 creates aline of weakness in the rupturable portion along which the disk materialwill tear when exposed to a fluid having a predetermined pressure. Whilethe presently preferred embodiment provides the score line on the domeitself, the score line may be provided in other locations, such as, forexample, the transition area between the dome and the flange of the diskor on the flange itself.

[0051] Referring again to FIG. 1, a positioning pin 68 preferablyextends between inlet support member 30 and outlet support member 32 andthrough flange 48 of rupture disk 44. Positioning pin 68 ensures thatinlet support member 30 is properly aligned with outlet support member32 and that rupture disk 44 is properly positioned between supportmembers 30 and 32. When the assembly is properly positioned, inlet bore34 aligns with outlet bore 36 to create a fluid passageway that isblocked by rupturable portion 45 of rupture disk 44. Additionalpositioning pins may be placed in a symmetrical or asymmetrical patternaround the support members to further control the relative positions ofthe rupture disk and support members.

[0052] A series of cap screws 40 (only one of which is illustrated inFIG. 1) are disposed through bolt holes 41 to engage internally threadedbolt holes 43. Preferably, bolt holes 41 in outlet support member 32include a counter bore 42 to receive the head of cap screw 40. Theengagement of cap screws 40 with bolt holes 41 and 43 draws outletsupport member 32 towards inlet support member 30 to sealingly engageflange 48 of rupture disk 44.

[0053] Preferably, inlet support member 30 includes a raised seatingsurface 78 and outlet support member 32 includes a corresponding seatingsurface 79 to engage flange 48 of rupture disk 44. It is contemplatedthat seating surface 78 may include a bite seal, or other similarsealing device, to create a seal with the flange. Alternatively, ano-ring or gasket may be positioned between inlet support member 30 andflange 48 to create the seal.

[0054] As is shown in FIG. 1, pressure relief assembly 20 is positionedbetween a circular inlet pipe 22 and a circular outlet pipe 28. Inletpipe 22 includes an inlet fluid pathway 64 and an inlet pipe flange 24.Outlet pipe 28 includes an outlet fluid pathway 66 and an outlet pipeflange 26.

[0055] Preferably, inlet pipe flange 24 includes a raised surface 74that engages a corresponding surface 75 on inlet support member 30 andoutlet pipe flange 26 includes a raised surface 76 that engages acorresponding surface 77 on outlet support member 26. A series of boltmembers 60 draw inlet pipe flange 24 towards outlet pipe flange 26 tocreate a seal with the pressure relief assembly 20.

[0056] Preferably, a U-shaped positioning fixture 38 extending frominlet support member 30 engages an opening 58 in inlet pipe flange 24 toensure pressure relief assembly 20 is properly oriented between the pipeflanges. U-shaped positioning fixture 38 also ensures that inlet supportmember 30 is placed adjacent inlet pipe flange 24 and, thus, preventspressure relief assembly 20 from being installed upside down in the pipeflanges. Pressure relief assembly 20 is properly positioned betweeninlet pipe flange 24 and outlet pipe flange 26 when inlet fluid pathway64 aligns with inlet bore 34, outlet bore 36, and outlet fluid pathway66 to create a fluid passageway that is blocked by rupturable portion 45of rupture disk 44.

[0057] Inlet pipe 22 is connected to a system or vessel (not shown) thatcontains a pressurized fluid. The fluid may be in either gas or liquidform. Inlet pipe 22 conducts the pressurized fluid to pressure reliefassembly 20 and the exposed rupturable portion 45 of rupture disk 44.Rupturable portion 45 is configured to burst when the pressure of thefluid reaches a predetermined level that is indicative of anover-pressurization in the system or vessel. The burst pressure of thedisk may be controlled by varying different parameters of the diskdesign, including, but not limited to, the height of the domed section,the thickness of the disk, and the depth and location of the score line.

[0058] When the disk bursts and tears along score line 80, an openingthrough the disk is created. The opening allows the fluid to flow frominlet bore 34 to outlet bore 36 and into outlet fluid pathway 66,thereby reducing the pressure in the system or vessel. Outlet fluidpathway 66 may release the fluid to the environment or to a safetyreservoir (not shown) depending upon the nature of the fluid in thesystem or vessel.

[0059] In accordance with the present invention, the pressure reliefassembly includes a safety member disposed adjacent the concave surfaceof the rupture disk. The safety member includes a hinge having a knucklethat extends downwardly into the dome area created by the rupturableportion of the disk and extends laterally across the dome area to apoint that is inside the area circumscribed by the score line or insidethe area circumscribed by an arc connecting the two ends of the scoreline. A tongue extends away from the knuckle and into the outlet bore ofthe outlet support member in a direction generally perpendicular to theflange of the safety member. Preferably, the tongue extends past theflange of the safety member, although the end of the tongue maygenerally align with plane created by the flange. The present inventioncontemplates that the hinge may be angled with respect to the flange,such that the hinge extends into the outlet bore and towards the outletsupport member. It is further contemplated that the hinge may have agenerally flat configuration.

[0060] As illustrated in FIG. 1, a safety member 50 is positionedbetween rupture disk 44 and outlet support member 32 and generallysupports the transition area of the rupture disk. Preferably, safetymember 50 is a separate structure from rupture disk 44 and from outletsupport member 32. It is contemplated, however, that safety member 50may be integral with or connected to either rupture disk 44 or outletsupport member 32 with spot welds or in any other manner to keep thestructures together.

[0061] Safety member 50 includes a flange 62 and a hinge 52. Flange 62of safety member 50 has substantially the same general shape as flange48 of rupture disk 44 and is sealed in pressure relief assembly 20between the rupture disk flange and outlet support member 32.Preferably, as shown in FIG. 2, flange 62 includes a series of holes 82that may be engaged by positioning pin 68 (referring to FIG. 1).

[0062] As shown in FIG. 3a, hinge 52 includes a knuckle 53 and a tongue54. Knuckle 53 extends from flange 62 into dome area 35. In theillustrated embodiment, knuckle 53 is linear in cross-section. It iscontemplated, however, that knuckle 53 may have other cross-sections,such as, for example, a curved cross-section that generally follows thecontour of the rupturable portion. Preferably, knuckle 53 does notcontact rupturable portion 45 and, thus, leaves a gap 51 between theknuckle and the rupturable portion. It is contemplated, however, thatknuckle 53 may contact rupturable portion 45 when the rupture disk is inan unruptured state.

[0063] Referring to FIGS. 1 and 2, the outer edge of knuckle 53 extendsdownwardly into dome area 35. Outer edge 53 also extends laterallyacross dome area 35 to a point that is inside the area circumscribed byscore line 80 or inside the area circumscribed by an arc connecting theends 84 and 86 of score line 80. The outer edge of knuckle 53 forms agenerally straight line about which the rupturable portion will bendwhen the rupture disk ruptures. In a presently preferred embodiment, theouter edge 53 extends to a point inside, but directly adjacent to thearea circumscribed by the score line 80 or the area circumscribed by anarc 85 connecting the two ends of the score line. This embodiment of thehinge prevents fragmentation, yet maximizes the size of the openingcreated when the disk ruptures, thereby minimizing the pressure drop, orvelocity head loss, over the ruptured disk and achieving a low flowresistance, K_(r).

[0064] As shown in FIG. 4, hinge 52 is formed with a first pocket 90 anda second pocket 92. First and second pockets preferably have a concaveshape that faces gap 51 (referring to FIG. 3b) between knuckle 53 andrupturable portion 45 of rupture disk 44. Preferably, first and secondpockets 90 and 92 are positioned adjacent first and second ends 84 and86 of score line 80, respectively. It is contemplated that first andsecond ends 84 and 86 of score line 80 may terminate at a point directlybelow first and second pockets 90 and 92, respectively (as illustratedin FIG. 2). Alternatively, first and second ends 84 and 86 of score linemay terminate at a point that is directly aligned with or just short offirst and second pockets 90 and 92, respectively.

[0065] As illustrated in FIGS. 1-4, tongue 54 extends away from knuckle53 and into outlet bore 36. Preferably, as shown in FIG. 2, tongue 54includes a main linear section 55 with two substantially straight sideflaps 56 that project from the main linear section 55 towards the outletsafety member 32. Preferably, as shown in FIG. 2, the angle 87 betweenside flaps 56 and main linear section 55 is obtuse, although the presentinvention contemplates that angle 87 may be a right angle or an acuteangle. More preferably, angle 87 is greater than the angle between mainlinear section 55 and a line of radius 89 extending through thecorresponding end of main linear section 55. Still more preferably,angle 87 is within the range of about 130° to 160°.

[0066] In the embodiment illustrated in FIG. 1, side flaps 56 extendtowards outlet safety member 32. Preferably, side flaps 56 are in closeproximity to, but do not contact outlet safety member 32 when the diskis in an unruptured state.

[0067] In an alternative embodiment, and as illustrated in FIG. 3b,tongue 54 includes a tongue support 57 that projects from the end of thetongue towards outlet support member 32. Preferably, tongue support 57extends to a point that is in close proximity to, but not in contactwith, outlet support member 32. It is contemplated that otherembodiments of the support structure will be readily apparent to oneskilled in the art.

[0068] Referring to FIG. 2, safety member 50 preferably includes aseries of stress risers 88. Each stress riser 88 extends away fromflange 62 and into dome area 35 of rupturable portion 45 of the rupturedisk. Each stress riser 88 terminates in one or more stressconcentrating points. Preferably, the stress concentrating points of atleast two of the stress risers are aligned with score line 80 inrupturable portion 45 of the rupture disk. The stress concentratingpoints, as explained in greater detail below, contact the rupturableportion of the rupture disk when the rupture disk reverses to ensure therupturable portion tears to create a flow path for fluid to escape.

[0069] The safety member may include recessed, or “scalloped out,” areasbetween each stress riser. These “scalloped out” areas create gaps inthe support of the transition area of the rupture disk. As alsoexplained in greater detail below, the gaps in the support of therupture disk also help ensure that the rupturable portion tears tocreate a flow path for fluid to escape. These scalloped out areas may belocated at a few selected locations around the safety member annulus ormay alternatively be regularly spaced around the entire annulus orsubstantially the entire annulus (e.g. exclusive of the hinge area).

[0070] As described above and referring to FIG. 1, inlet fluid pathway64 conducts pressurized fluid, in either gas or liquid form, to inletbore 34 and to rupturable portion 45 of rupture disk 44. In theillustrated embodiment, the pressurized fluid contacts convex surface 47of rupture disk 44, thereby placing the material of the disk under acompressive force. The magnitude of the compressive force corresponds tothe pressure of the fluid. When the pressure of the fluid reaches apredetermined level and the compressive force exceeds the structural andmaterial strength of the rupturable portion of the rupture disk, thedome-shaped section will begin to buckle, or reverse.

[0071] As illustrated in FIG. 5, the reversal of the disk will cause thedisk to tear along score line 80 to form a disk petal 103 that has ashape defined by score line 80 and a disk hinge 102 that connects diskpetal 103 to flange 48 to prevent the disk from fragmenting. Under thecontinued fluid pressure, disk hinge 102 will bend, with respect to theflange, through gap 51 towards safety member 50. Because knuckle 53 ofsafety member 50 is close to disk hinge 102, the momentum gained by thedisk hinge will be relatively small and will be arrested by the eventualcontact with the knuckle before the disk petal gains enough momentum totear away from the disk hinge.

[0072] If the disk does not tear along the score line during the initialbuckling of the disk, the disk will continue to buckle and reverse underthe pressure of the fluid until the disk contacts the stressconcentrating points of stress risers 88. The stress concentratingpoints will increase the stress in the score line 80 to facilitateopening of the disk. In addition, the unsupported gaps of the transitionarea, as defined by the shape of the “scalloped out” areas of the safetymember, create additional forces in the rupturable portion of the diskto ensure the disk opens to create a vent path for the fluid.

[0073] After the rupturable portion tears and the disk hinge 102 issupported by knuckle 53, the force of the fluid pressure and themomentum of disk petal 103 will cause the disk to bend around the outeredge of knuckle 53. The petal will continue to bend around knuckle 53until contacting tongue 54 of hinge 50. The contact of disk petal 103with tongue 54 will bend the tongue until side flaps 56 contact outletsafety member 32. The portions of disk petal 103 that extend on eitherside of tongue 54 will wrap around the tongue and contact side flaps 56.

[0074] Depending upon the pressure in the system and the momentum withwhich the petal is moving, tongue 54 and side flaps 56 may further bendand deform with the contact of disk petal 103 to absorb the kineticenergy of the moving disk petal and stop the movement of the disk petal.Preferably, side flaps 56 are angled with respect to the outlet supportmember so that they may bend outwardly, or inwardly depending upon angle87, if the force of contact with the moving petal is great enough. Byabsorbing the kinetic energy of the moving disk petal, the tonguereduces the overall force on the disk petal, thereby preventing the diskpetal from fragmenting. The dimensions of the hinge and, in particular,the dimensions of the knuckle and tongue, are selected so that the hingewill effectively absorb the kinetic energy of the disk petal, whileachieving a large and unobstructed flow path through which thepressurized fluid may vent.

[0075] In the illustrated embodiment, the portions of the disk petalsurrounding the end of the score line will fold into pockets 90 and 92of hinge 50. Pockets 90 and 92 extend generally away from the flange 62of the safety member and in the direction of the outlet bore. Pockets 90and 92 have curved surfaces and are configured to receive the portionsof the rupture disk adjacent the respective ends 84 and 86 of score line80 without creating any additional stress concentrating points. Thepockets provide support for the rupture disk material adjacent the endsof the score line. This reduces the tensile forces acting on the ends ofscore line to prevent the tear in the rupture disk from continuing pastthe ends of the score line. Thus, the pockets help in preventing thepetal from completely separating from the disk. In a preferredembodiment, the disk reverses symmetrically and the disk will wraparound the opposing pockets at the same time thereby preventing thecreation of any uneven stresses in either side of the disk hinge.

[0076] The opening created by the rupture of the disk will be defined bythe shape and location of the score line and by the shape and locationof the hinge. In the preferred embodiment, the score line and hinge areconfigured to maximize the size of the opening. It is contemplated thatthe shape of the hinge, as defined by the first pocket, the secondpocket, and the outer edge of the knuckle, may be a generally straightline Alternatively, as illustrated in FIG. 2, the outer edge of theknuckle may be generally straight and the pockets, disposed on eitherside of the knuckle, may angle towards the flange of the safety member.

[0077] In the preferred embodiment and as illustrated in FIG. 4, theouter edge of the knuckle 53 includes a generally straight section thatis located at a point minimally inside the ends of the score line 80.The straight section may be inside, but directly adjacent to the area 83circumscribed by the score line 80. Alternatively, the straight sectionmay be inside, but directly adjacent to the area transcribed by an arc85 connecting the ends 84 and 86 of score line 80. The line 85 appearsfor purposes of illustration in the drawings and does not actuallyappear on the disk.

[0078] When disk petal 103 bends around the outer edge 53 of hinge 50,the bending portion of the petal will preferably form a generallystraight line between the ends 84 and 86 of score line 80. Thus, amaximal portion of disk petal 103 will bend out of the fluid passageway.In this manner, the size of the opening created when the disk

[0079] In another embodiment and as illustrated in FIGS. 17 and 18,safety member 50 is generally flat. In certain applications, such as,for example, electrical switchgear, the space available for the pressurerelief assembly necessitates that the outlet safety head and hinge bereplaced with a flat plate that can be bolted or otherwise directlyattached to the system. To help prevent a rupture disk from fragmentingin these situations, a hinge may be defined in the flat plate.

[0080] As illustrated in FIG. 17, safety member 50 includes a hinge 52.Hinge 52 includes a tongue 53 that defines a generally straight outersection and a pocket 190 and 192 on either side of the hinge. In theillustrated embodiment, hinge 52 lies in the same plane as flange 62.The present invention contemplates, however, that hinge 52 may be bentto extend downwardly into the dome of the rupture disk or upwardly awayfrom the concave side of the disk dome. In addition, the outer edge ofthe hinge may have a curved shape.

[0081] Preferably, flange 62 includes a series of bolt holes (not shown)to allow safety member 50 to be directly connected to the pressurizedsystem. The flange of the rupture disk may be attached to flange 62 ofthe rupture disk with an adhesive or through welding.

[0082] Pockets 190 and 192 are positioned adjacent first and second ends84 and 86 of score line 80 (referring to FIG. 2). It is contemplatedthat first and second ends 84 and 86 of score line 80 may terminate at apoint directly below first and second pockets 190 and 192.Alternatively, first and second ends 84 and 86 of score line mayterminate at a point that is directly below the edge of hinge 53 thatdefines first and second pockets 190 and 192.

[0083] As described in greater detail above, when the rupture diskopens, petal 103 of the rupture disk will bend around hinge 52 to absorbthe energy of the disk opening. Hinge 52 may bend with petal 103 as therupture disk opens to further absorb the energy of the disk opening.Preferably, safety member 50 also includes stress risers 88 that, asalso described above, ensure the rupture disk fully opens along thescore line.

[0084] The portions of the disk petal surrounding the ends of the scoreline will fold into pockets 190 and 192. This will reduce the magnitudeof the stresses acting on the ends of the score line to prevent the tearin the rupture disk from continuing past the ends of the score line andultimately causing the disk petal to fragment.

[0085] Another factor in obtaining a large and unobstructed opening inall service conditions is controlling the initial reversal point of thedisk. The initial reversal point of the disk is the point at which thedisk initially buckles under the force of the pressurized fluid. In onepreferred embodiment, the initial reversal point is positioned at theapex of the dome shaped rupturable portion. This is a central positionon the rupture disk and also the position on the rupturable portion thatis the furthest from the transition area of the disk. Initiatingreversal at this point ensures that the disk reverses in a symmetricalfashion.

[0086] A symmetrical disk reversal will result in an enhanced diskopening for both scored and unscored disks. In a scored disk, thesymmetrical reversal ensures that an equal force is distributed alongthe entirety of the score line so that the disk material will tearcompletely along the score line and fully open. In an unscored disk,where a secondary cutting mechanism, such as perimeter teeth, are usedto puncture and open the disk, the symmetrical reversal ensures that thedisk material will fold evenly over the secondary cutting mechanism. Thesecondary cutting mechanism will then cause the disk to fully open andallow the disk petal to bend around the disk hinge and maximize the sizeof the opening.

[0087] In accordance with the present invention, the dome of therupturable portion includes a structural apex formation. A structuralapex formation of the present invention will introduce a structuralweakness, such as, for example, a thinning or stretching of the diskmaterial, into the rupturable portion of the rupture disk. The thinningor stretching of the disk material compromises the structural integrityof the disk dome. It has been found that when the disk is subject to afluid having a certain pressure, the rupture disk will initiate itsreversal at the structural weakness. Thus, a properly configuredstructural apex formation will control the initial reversal point of thedisk.

[0088] It should also be noted that a structural apex formation willreduce the expected burst pressure of the rupture disk. In other words,a disk that has a structural apex formation will burst at a lowerpressure than a similar disk without a structural apex formation. Thisis noteworthy in that a disk without a structural apex formation must bemade from a thinner material in order to achieve the same burst pressureas a disk with a structural apex formation. It has also been found thata correlation exists between the size and shape of the structural apexformation and the amount of reduction in the burst pressure. In general,a larger structural apex formation will result in a greater reduction inburst pressure.

[0089] The concept of the structural apex formation offers the potentialfor great improvement in the reliability and accuracy of rupture disks,particularly those disks configured to rupture at low pressures. The lowpressure disks must typically be made from a thin material, which iseasily damaged. Any damage to the disk prior to or during installationcan dramatically alter the burst pressure of the disk. In addition, anyirregularities in the installation, such as misalignment of safety headsor of the disk itself, heat induced irregularities, and bolt or flangeinsensitivity, can further alter the burst pressure of the disk. Since adisk with a structural apex formation can be made from a thickermaterial that is less susceptible to these types of problems, theintroduction of a structural apex formation will improve the reliabilityof the rupture disks.

[0090] In addition, it has been found that the size and shape of thestructural apex formation will be the determining factor in determiningthe burst pressure of the rupture disk. In other words, theconfiguration of the structural apex formation will override otherdesign factors, such as, for example, the depth and location of thescore line, that previously affected the burst pressure of the rupturedisk.

[0091] As shown in FIGS. 6 and 7, the structural apex formation ispreferably an indentation 140 located at the apex of the domed shape ofthe rupturable portion. Preferably, as shown in FIG. 7, indentation 140is formed in convex surface 47 of the dome, creating a cavity 143 in theconvex surface 47 and a corresponding nipple-shaped protrusion/dimple144 in the concave surface 46. Alternatively, indentation 140 may beformed in the concave surface 46 of the dome, creating a cavity in theconcave surface 46 and a corresponding nipple-shaped protrusion in theconvex surface 47.

[0092] As shown in FIG. 7, indentation 140 includes a circular outeredge 142. Preferably, the distance from the outer edge 142 to transitionarea 49 is the same at all points along outer edge 142 of indentation140.

[0093] As shown in FIGS. 8 and 9, the indentation may have a variety ofshapes. For example, as illustrated in FIG. 8, indentation 140 may be astraight line having a midpoint coinciding with the apex of the dome. Inaddition, as shown in FIG. 9, indentation 140 may include two straightlines that intersect at the apex of the dome.

[0094] It is contemplated that changing the size and shape of thestructural apex formation can produce wide variations in the pressure atwhich a disk of given size and material will burst. For example, a 1″disk made of 0.003″ thick material having a small indentation will burstat a higher pressure than a similar disk with a larger indentation.Thus, altering the configuration of the structural apex formation allowsa particular size and thickness rupture disk to be adapted to theparticular pressure relief needs of a variety of different commercialapplications.

[0095] It should be noted, however, that to produce a rupture disk thatwill accurately burst at the desired pressure, the indentation, or otherstructural apex formation, must be formed in a manner that ensures thatthe configuration of the structural apex formation is consistent betweendisks. One method of forming an indentation in a rupture disk isdescribed in U.S. Pat. No. 6,006,938 to Mozely. In the method describedtherein, the indentation is “free-formed” in that a tool is impactedwith the disk as the disk is being formed, without any additionalsupport for the rupture disk. As shown in the test data set forth below,the rupture disks formed according to this method will not consistentlyburst at a desired pressure. This method, therefore, will not produce adisk with the high level of burst pressure accuracy that is demanded bymany commercial applications.

[0096] In accordance with the present invention, an apparatus forforming an indentation in the dome of a rupture disk is provided. It iscontemplated that the indentation may be formed at any stage in themanufacture of the disk. Accordingly, the present invention is directedto an apparatus for forming an indentation in a formed rupture disk or arupture disk blank and to an apparatus for forming an indentation in arupture disk as the dome of the disk is being formed. The indent formingapparatuses allow indentations to be formed in rupture disks in areliable and consistent manner, which, as set forth in the test databelow, results in an improvement in the burst accuracy of the rupturedisks.

[0097] As illustrated in FIG. 10, an indent forming apparatus 148includes a first member, which is preferably an anvil 154. Anvil 154includes a support surface 155 that defines and opening 164. Preferably,opening 164 is circular, although it is contemplated that opening 164may have other shapes.

[0098] Support surface 155 is configured to engage one side ofrupturable portion 45 at the apex of the domed shape such that opening164 encompasses the apex. It is contemplated that support surface 155may have a small width such that only a selected portion of rupturableportion 45 is supported. Alternatively, support surface 155 may have ashape that conforms to the contour of the rupture disk dome and extendsto the transition area of the disk, such that the entire rupturableportion 45, outside of opening 164, is supported.

[0099] Preferably, support surface 155 engages the concave side of thedomed shape, although the support surface may engage the convex side ofthe domed shape. Alternatively, the anvil may engage one side of arupture disk blank that, as described in greater detail below, willeventually be formed into a rupture disk.

[0100] In the illustrated embodiment, the centerline 162 of anvil 154 isaligned with the apex of the domed shape of rupturable portion 45. It iscontemplated, however, that centerline 162 may be offset from the apexof the dome shape.

[0101] A frame 156 surrounds anvil 154. Frame 156 includes an inner wall158 that defines a cavity configured to receive flange 48 of the rupturedisk. Preferably, the height of inner wall 158 is chosen to ensure thatflange 48 does not contact the bottom surface 159 of the cavity so thatanvil 154 is the only source of support for the rupture disk. Inaddition, the diameter of inner wall 158 closely corresponds to thediameter of flange 48. In this manner, inner wall 158 ensures that therupture disk is correctly aligned on anvil 154.

[0102] Frame 156 may include one or more pins 160 (only one pinillustrated in FIG. 10). Pins 160 are configured to engage holes 88 inflange 48 (referring to FIG. 6). The engagement of pins 160 with holes88 further ensures that the rupture disk is correctly aligned on anvil154.

[0103] The indent forming apparatus 148 also includes a second member,which is preferably a punch 150 that is generally aligned with opening164 in anvil 154. In the illustrated embodiment, the centerline 166 ofpunch 150 is directly aligned with the centerline 162 of the anvil. Thepresent invention contemplates, however, that the punch 150 may beoffset with respect to the apex and/or the anvil, provided that thepunch tip is within the area circumscribed by anvil opening 164.

[0104] Punch 150 includes a tip 152 that engages the second side ofrupturable portion 45. As punch 150 moves relative to anvil 154, thematerial of the rupturable portion corresponding to opening 164 isdisplaced relative to the anvil 154. This forced and controlleddisplacement causes the disk material along the edge and downslopingsection of the indentation to deform, by stretching, thinning, orshearing, relative to the surrounding disk material.

[0105] The supporting force of the anvil, which opposes the force of thepunch, will create a permanent deformation, such as a crease 200(referring to FIG. 19) in the surface of rupturable portion 45. Thispermanent deformation is created as the punch forces a displacement ofthe material of the rupturable portion relative to the material that issupported by the anvil. Preferably, the concave surface of the disk issupported by the anvil and, thus, the deformation will be formed in atleast the concave surface. It is contemplated that the deformation mayalso be formed in the convex surface or in both the concave and convexsurfaces.

[0106] The deformation, stretching, thinning, or shearing of the diskmaterial creates the structural weakness in the disk dome. By preciselycontrolling the movement and location of the punch and anvil, similaramounts of thinning, stretching, or shearing may be induced insuccessive disks. In this manner, the reliability and accuracy of aseries of rupture disks may be maintained at a level required forcommercial application.

[0107] Preferably, the motion of punch 150 is precisely controlled. Inthe preferred embodiment, the allowable range of motion of punch tip 152is governed by a micrometer, which allows for adjustments of 0.0001″. Inthis manner, the depth of the indent, with respect to the apex of thedome, that is created in the rupture disk may be accurately andprecisely controlled.

[0108] Alternatively, punch tip 152 and anvil opening 164 may be closelysized so that the disk material is displaced in shear. As illustrated inFIG. 19, indentation 140 formed by shearing rupturable portion 45results in outer edge 142 having a sharp corner. In addition, a crease200 is formed on the opposite side of rupturable portion 45, which inthe illustrated embodiment is the concave surface. The shearing actionof the punch also creates a well-defined thinned area 202 in therupturable portion 45. This thinned area represents the structuralweakness that will coincide with the point of initial reversal.

[0109] As illustrated in FIG. 11, a punch tip 152 for shearing thematerial of rupturable portion 45 preferably includes a concave surface168. When punch tip 152 is engaged with rupturable portion 45, edge 167first engages the curving surface of the rupturable portion. Thisensures that each indentation formed in subsequent rupture disks willhave essentially the same shape. A flat punch tip will wear down withuse and may eventually result in uneven and inconsistent indentations.

[0110] The profile of punch tip 152 may have any shape or size. Forexample, as illustrated in FIGS. 12a-12 c, punch tip 152 may have acircular profile (referring to FIG. 12a), a D-shaped profile (referringto FIG. 12b), or a tear drop profile (referring to FIG. 12c). The shapeof anvil opening 164 may or may not be configured to correspond to theprofile of punch tip 152. For example, a tear drop shaped punch profilemay be used in conjunction with either a circular anvil opening or atear drop shaped anvil opening.

[0111] The present invention contemplates that the configuration ofindentation 140 may be varied through any number of variances in theindent forming apparatus. For example, the size and shape of punch tip152 and anvil opening 164 may be varied alone or in combination to alterthe resulting shape of the indentation. In addition, one or both ofpunch tip 152 and anvil opening 164 may be offset from the apex of thedome shape to further vary the configuration of the indentation. It isexpected that continued experimentation with differently shaped andsized punch tips and anvil openings will result in an indentationconfiguration that provides optimal performance characteristics.

[0112] An apparatus 160 for forming an indentation in the rupturableportion as the rupture disk is formed is illustrated in FIGS. 13 and 14.As is known in the art, rupture disks are typically manufactured from aflat, circular sheet of material known as a rupture disk blank. Aportion of the flat sheet of material is subject to a pneumatic orhydraulic pressure to form the dome-shaped rupturable portion.

[0113] Apparatus 160 includes a clamp 161 that securely holds theperimeter of a disk blank (identified as dashed line 172). Clamp 161includes a support 162 and a mold 164. Support 162 includes a centralpassageway 168 connected to a source of pressurized fluid. When the diskblank is securely fastened in clamp 161, passageway directs thepressurized fluid (as indicated by arrows 170) against the central,unclamped portion of the disk blank. The force of the fluid acts on theunclamped material of the disk blank to displace the unclamped materialrelative to the clamp and into mold 164.

[0114] Mold 164 includes a concave surface 176 that faces the diskblank. As the unclamped material is displaced relative to the clamp, thematerial engages concave surface 176. The shape of concave surface 176defines the resulting shape of rupturable portion 45.

[0115] Mold 164 includes an opening 150 that houses a member, which ispreferably a punch 150. Punch 150 includes a tip 152 that projects fromconcave surface 176 at or near a point that corresponds to the apex ofthe domed shape. Preferably, punch 150 is moveable with respect to mold164 to vary the distance by which punch tip 152 projects from concavesurface 176. Mold 164 also includes a vent 174 to allow the pressurizedfluid to escape if any problems occur during the formation of therupture disk.

[0116] As illustrated in FIG. 14, punch tip 152 engages the material ofthe disk blank as it is displaced by the pressurized fluid. Thecontinued force of the fluid on the blank material causes the materialto deflect around the punch tip, resulting in the formation ofindentation 140. The shape of indentation 140 and of indentation edge142 may be altered by varying the pressure of the forming fluid. Ahigher fluid pressure will result in a sharper radius of curvature inindentation edge 142. Conversely, a lower fluid pressure will result ina greater radius of curvature in indentation edge.

[0117] By forming the rupture disk into the mold and punch combination,the resulting configuration of the indentation can be preciselycontrolled. In particular, the depth of the indentation, with respect tothe apex of the dome, can be precisely controlled. In addition, theheight of the dome with respect to the disk flange, which is anotherfactor that has a significant impact on the burst pressure of the disk,can be precisely controlled. Thus, the reliability and accuracy of therupture disks can be maintained at a level required for commercialapplications.

[0118] The present invention contemplates that punch tip 152 may have across-sectional shape as illustrated in FIG. 11, and any profile,including, for example, those profiles illustrated in FIGS. 12a-12 c. Itis further contemplated that the punch tip may be offset from the apexof the domed shape.

[0119] The configuration of indentation 140 may also be varied by movingthe punch tip and reforming the disk dome. After the disk is formed witha fluid at a first pressure, punch tip 152 may be retracted, partiallyor fully, with respect to the concave shape of the mold. The rupturedisk is then subject to pressurized fluid at a second pressure, which ispreferably less than the original forming pressure. The pressurizedfluid will again act on the disk to reform the dome. Since the punch tipis no longer engaged with the rupturable portion, the fluid will act todecrease the depth of the indentation relative to the apex of the domedshape. In this manner, the configuration of the indentation may bealtered.

[0120] The present invention further contemplates that a rupture diskdome having an indentation may be hard stamped from a rupture diskblank. This would be achieved by tooling that is configured to createthe desired shape of the rupture disk dome from the rupture disk blank.In this embodiment, the punch is slidably disposed in the tooling. Thiswould allow the depth of the indent, relative to the apex of the dome,to be changed between disks having similar dome heights and shapes. Asdiscussed above, the configuration of the indentation determines theburst pressure of the rupture disk. Thus, the burst pressure ofotherwise similar disks may be easily modified to meet the needs ofdifferent commercial applications.

[0121] Alternatively, as illustrated in FIGS. 15 and 16, the structuralapex formation may be an opening 180 in rupturable portion 45 of therupture disk. As shown in FIG. 15, opening 180 is preferably centered atthe apex of the domed shape of rupturable portion 45. It iscontemplated, however, that opening 180 may be offset from the apex ofthe domed shape.

[0122] As illustrated in FIG. 15, opening 180 is preferably circular.The present invention contemplates, however, that opening 180 may haveother shapes, such as, for example, a triangle, square, pentagon,hexagon, or oval.

[0123] As illustrated in FIG. 16, a liner 182 covers and seals opening182. Preferably, liner 182 is made of a material that is lighter andmore flexible that the material of the rupture disk. Preferably, liner182 covers the entire rupture disk, although liner 182 may only extend ashort distance past opening 182. Liner 182 may be attached with anadhesive material or through welding to any part of the rupture disk,including the rupturable portion and/or the flange.

[0124] It has been found, as evidenced in the examples below, thatindenting the dome of the disk at the apex in accordance with themethods and apparatus of the present invention improves the burstaccuracy of the rupture disk. Rupture disks are manufactured in lots ofa given number (typically 5-10 pieces) and all disks within a lotreceive a rated rupture pressure based on a statistical sampling of testdisks from the same manufacturing lot. Typically, all of the diskswithin the lot will rupture within 5% of the rated rupture pressure.Thus, to prevent premature rupture of the disk, the operating pressureof the system should not exceed 90% of the rated rupture pressure of thedisk. Increasing the accuracy and repeatability of the disk will allowthe system to be operated at higher than 90% of the rated pressure ofthe rupture disk and still achieve an acceptable safety margin.

[0125] Rupture disks according to the present invention are considerablymore consistent in their actual rupture pressure. The following burstaccuracy test data represents comparative testing done on rupture diskshaving an indentation formed in one of three different methods: (1) freeformed indent, (2) mold formed indent; and (3) anvil formed indent.

[0126] Burst Accuracy Test 1—Disks with Free Formed Indentation:

[0127] This burst accuracy testing was performed on 1.5″ disks having anindentation formed with a “free form” method where a tool was engagedwith the disk dome during formation, without the use of a mold or othersupport. Several configurations of disks having various thicknesses,dome heights, and indent depths were burst to determine the actual burstpressure of each disk. The actual burst pressures for each configurationof disk were then compared to determine the burst accuracy for that diskconfiguration. Dome Indent Avg. Burst Test Disk Size Thickness HeightDepth Nbr. of Pressure Burst Pressure No. (inches) (inches) (.001″)(.001″) Samples (psi) Accuracy* 1 1.5 0.003 126 14.2 10 15.4 5.6 2 1.50.003 152 5.2 8 18.1 2.3 3 1.5 0.007 251 14.3 6 150 1.0 4 1.5 0.007 15011 7 95 5.0 5 1.5 0.007 142 1 8 122 4.7 6 1.5 0.007 256 17 10 155 2.8 71.5 0.01 207 3.7 5 318 2.0 8 1.5 0.01 274 5.1 7 401 4.7 9 1.5 0.01 234 810 353 3.1 10  1.5 0.01 207 3.7 5 305 5.2 11  1.5 0.0025 152 12.5 4 10.25.1 12  1.5 0.004 155 12 8 28.4 5.9 13  1.5 0.004 145 3 8 35.2 7

[0128] Accuracy Test 2—Disks with Mold Formed Indentation:

[0129] This burst accuracy testing was performed on 1.5″ disks having anindentation formed with a mold as described in greater detail above.Several configurations of disks having various thicknesses, domeheights, and indent depths were burst to determine the actual burstpressure of each disk. The actual burst pressures for each configurationof disk were then compared to determine the burst accuracy for that diskconfiguration. Dome Indent Avg. Burst Test Disk Size Thickness HeightDepth Nbr. of Pressure Burst Pressure No. (inches) (inches) (.001″)(.001″) Samples (psi) Accuracy* 1 1.5 0.003 289 8.9 12 38.2 2.8 2 1 5.003 136 10.4 20 15.1 2.6 3 1 5 .006 140 6.7 20 75.7 2.9 4 1.5 0.007 14410.7 10 114 1.9 5 1 5 0.007 268 2.7 5 215 1.3 6 1.5 0.0025 143 1.2 514.7 4.6 7 1.5 0.003 289 8.9 12 38.8 2.2 8 1.5 0.003 289 9.3 8 38.3 2.99 1.5 0.003 289 8.8 7 38.5 2.9 10  1.5 0.003 291 3.7 7 46.4 2.4 11  1.50.003 291 2.8 6 58.1 2.7 12  1.5 0.003 291 9.1 5 37.6 3.3 13  1.5 0.003287 7.1 10 51.3 2.1

[0130] Burst Accuracy Test 3—Disks with Anvil Formed Indentation:

[0131] This burst accuracy testing was performed on 1″ disks having anindentation formed with an anvil after formation of the disk dome, asdescribed in greater detail above. Several configurations of diskshaving various thicknesses, dome heights, and indent depths were burstto determine the actual burst pressure of each disk. The actual burstpressures for each configuration of disk were then compared to determinethe burst accuracy for that disk configuration. Dome Indent Avg. BurstTest Disk Size Thickness Height Depth Nbr. of Pressure Burst PressureNo. (inches) (inches) (.001″) (.001″) Samples (psi) Accuracy* 1 1 0.003190 23.6 9 22.56 2.59 2 1 0.003 190 25.5 9 22.43 2.5 3 1 0.003 190 27.69 22.40 2.92 4 1 0.003 190 29.5 9 22.39 1.95 5 1 0.003 190 29.5 9 22.262.79 6 1 0.003 190 31.4 9 21.79 2.79 7 1 0.004 190 n/a 10 50.63 2.20 8 10.003 250 n/a 5 35.24 4.3 9 1 0.011 190 n/a 5 310.1 3.8 10  1 0.011 250n/a 5 460.3 1.0 11  1 0.007 220 n/a 5 151.4 3.9

[0132] Burst Accuracy Summary

[0133] The following table summarizes the foregoing test data. Thistable presents the average of burst accuracies for the different methodsof forming an indentation in the dome of the rupture disk. IndentForming Method Average Burst Accuracy* Free Formed Indent 4.18 MoldFormed 2.66 Anvil Formed 2.79

[0134] As shown in the above testing and summarized in the precedingtable, rupture disks having an indentation formed in accordance with thepresent invention have a far greater burst accuracy than disks havingindentations formed with other methods.

[0135] Adjusting other design parameters of the disk, such as, forexample, the location of the score line, may provide additionalimprovements upon the burst accuracy of the disk. The present inventioncontemplates that a rupture disk having a structural apex formationconsistent with the present invention and a score line in the transitionarea of the disk will also have greatly improved burst accuracycharacteristics when compared to the burst accuracy characteristics ofconventional rupture disks.

[0136] Another benefit of the present invention is a reduced damagesafety ratio. The damage safety ratio of a disk is determined bydividing the actual burst pressure of a damaged disk by the ratedpressure of the disk. The following data represents the damage ratio ofrupture disks made according to the present invention with differenttypes of damage:

[0137] Damage Test: The following damage testing was performed on 1″rupture disks according to the present invention. These rupture diskswere made from 0.004″ Ni formed at 275 psig with a resulting 0.190″crown height. The average burst pressure of the disk batch tested in anundamaged state was 50.6 psig. According to ASME standards, anacceptable burst pressure tolerance is ±5 psig of the rated burstpressure. Thus, for the rupture disks of this test, the minimumacceptable burst pressure is 48.1 psig and the maximum acceptable burstpressure is 53.1 psig. Average Actual Burst Burst Pressure PressureDamage Damage Type* (psig) (psig) Ratio None 50.6 50.5 1.00 None 50.650.5 1.00 Blunt damage** to disk dome behind 50.6 51.0 1.01 hinge, sothat disk dome contacts midpoint of the knuckle Blunt damage to diskdome behind 50.6 51.0 1.01 hinge, so that disk dome does not contact theknuckle Blunt damage to the transition area 50.6 51.0 1.01 behind thehinge Blunt damage to the transition area 50.6 51.0 1.01 opposite thehinge Sharp damage*** to the transition area 50.6 49.7 0.98 behind thehinge Sharp damage to the transition area 50.6 50.5 1.00 opposite thehinge Sharp damage to the transition area over 50.6 51.0 1.01 one of thestress risers Sharp damage on score line opposite the 50.6 51.0 1.01hinge Blunt damage across score line opposite 50.6 42.5 0.84 the hingeBlunt damage across center of dome 50.6 25.0 0.49 Sharp damage to dome3.75 mm from 50.6 35.0 0.69 central indentation Sharp damage to dome 7.5mm from 50.6 45.0 0.89 central indentation

[0138] As shown in the above testing, a rupture disk made in accordancewith the present invention has a damage safety ratio of less thanabout 1. Thus, if a rupture disk according to the present invention isdamaged prior to or after installation, the disk will still rupture at apressure that is no greater than the maximum acceptable burst pressureof the disk (which, in this example, is the rated burst pressure plus5%).

[0139] As mentioned previously, the disclosed pressure relief assemblymay be used in a pressurized system containing either a pressurized gasor a pressurized liquid. In accordance with the present invention, arupture disk is provided that, when burst, has a low flow resistance,K_(r), in both a liquid application and a gas application.

[0140] The flow resistance, K_(r), of a rupture disk determines the rateat which the rupture disk will relieve fluid to reduce the pressure of asystem. The flow resistance is a function of the pressure drop, orvelocity head loss, over the burst rupture disk. A large velocity headloss results in a large K_(r) and, thus, a lower fluid release rate. TheAmerican Society of Mechanical Engineers (ASME), standard ASME PTC 25,have established performance testing requirements for fluid relief ratesof a rupture disk.

[0141] Rupture disks made in accordance with the present invention havea low K_(r) in both liquid and gas environments. The K_(r) rating of arupture disk is determined through a standardized procedure. In onemethod, the K_(r) rating of a particular disk design is determined bybursting three samples of three different sizes of the rupture disk atthe minimum pressure rating for the disk. The K_(r) value for each ofthe nine burst disks is then determined. Next, the average and thestandard deviation of the nine K_(r) values is determined. The K_(r)rating for the rupture disk is equal to the average of the nine K_(r)values plus three times the standard deviation of the nine K_(r) values.The following test data represents testing done on disks made inaccordance with the present invention in a gas environment according toASME standards: Disk Size Test No. K_(r) Value 1.0″ 1 0.256 1.0″ 2 0.2661.0″ 3 0.271 1.5″ 1 0.329 1.5″ 2 0.321 1.5″ 3 0.285 2.0″ 1 0.314 2.0″ 20.270 2.0″ 3 0.282 Average 0.288222 Standard Deviation 0.022074 K_(r)Rating 0.354444

[0142] As shown in the above testing, a rupture disk according to thepresent invention has a low K_(r) in a gas environment. While the K_(r)for a liquid environment may be slightly higher, the present inventionnonetheless provides for a low K_(r) value under liquid conditions.Preferably, the K_(r) of the rupture disk according to the presentinvention is less than about 1.6 in both gas and liquid applications.More preferably, the K_(r) of the rupture disk according to the presentinvention is less than about 1.0 in both gas and liquid applications.Even more preferably, the K_(r) of the rupture disk according to thepresent invention is less than about 0.7 in gas and/or liquidapplications.

[0143] An additional benefit of the present invention is a rupture diskdesign that provides low rupture pressures in a liquid application.Conventional non-fragmenting rupture disks are unsuited for low pressureliquid applications since the disks will not open fully in such anapplication. The rupture disk of the present invention, however, willmeet ASME performance standards in liquid applications having operatingpressures of under 100 psig.

[0144] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the rupture disk assembly ofthe present invention without departing from the scope or spirit of theinvention. Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. An apparatus for indenting a rupture diskincluding an annular flange and a rupturable portion having a domedshape, comprising: a first member having an opening, the first memberconfigured to engage a first side of the rupturable portion; and asecond member disposed on a second side of the rupturable portion andaligned with the opening in the first member, the second member operableto engage the rupturable portion at or near the apex of the domed shapeand to displace a section of the rupturable portion relative to thefirst member, thereby creating an indentation in the rupturable portionat or near the apex of the domed shape.
 2. The apparatus of claim 1 ,wherein the first member is an anvil and the second member is a punch.3. The apparatus of claim 2 , wherein the rupturable portion includes aconcave side and a corresponding convex side and the anvil engages theconcave side of the rupturable portion.
 4. The apparatus of claim 2 ,further including a frame having an inner wall defining a cavityconfigured to receive the flange of the rupture disk.
 5. The apparatusof claim 4 , wherein the diameter of the cavity closely corresponds tothe diameter of the flange such that the inner wall of the cavityensures the rupture disk is properly aligned on the anvil.
 6. Theapparatus of claim 5 , wherein the annular flange includes at least oneopening and the frame includes a pin configured to engage the opening toalign the rupture disk on the anvil.
 7. The apparatus of claim 2 ,wherein the punch includes a tip having a circular cross section and theopening in the anvil has a circular shape.
 8. The apparatus of claim 2 ,wherein the outer diameter of the punch tip has substantially the samesize as the opening in the anvil so that the section of the rupturableportion is displaced in shear.
 9. The apparatus of claim 2 , wherein thepunch includes a tip having a cross-sectional shape different from theshape of the opening in the anvil.
 10. The apparatus of claim 9 ,wherein the cross-sectional shape of the punch tip includes an arcconnected by a chord and the anvil opening is generally circular. 11.The apparatus of claim 9 , wherein the punch tip has a tear drop crosssection and anvil opening is generally circular.
 12. The apparatus ofclaim 2 , wherein the centerline of the opening in the anvil coincideswith the apex of the domed shape and the centerline of the punch isoffset from the apex of the domed shape.
 13. The apparatus of claim 2 ,wherein the punch includes a tip having a concave surface.
 14. A methodof forming an indentation in a rupture disk including an annular flangeand a rupturable portion having a domed shape, comprising the steps of:supporting a first side of the rupturable portion with a first memberhaving an opening; and engaging a second member aligned with the openingin the first member with a second side of the rupturable portion at ornear the apex of the domed shape to displace a section of the rupturableportion relative to the first member, thereby creating an indentation ator near the apex of the rupturable portion of the rupture disk.
 15. Themethod of claim 14 , wherein the first member is an anvil and thecenterline of the opening in the anvil is aligned with the apex of thedomed shape.
 16. The method of claim 15 , wherein the second member is apunch and the centerline of the punch is offset from the apex of thedomed shape.
 17. The method of claim 14 , wherein the second memberdisplaces the section of the rupturable portion in shear.
 18. The methodof claim 14 , wherein the second member displaces the section of therupturable portion a predetermined distance from the apex of the domedshape.
 19. The method of claim 14 , further comprising the step ofreforming the disk after the indentation is formed to reduce the depthof the indentation.
 20. A rupture disk having an indentation formed inaccordance with the process of claim 14 .
 21. A method of forming anindentation in a rupture disk, comprising the steps of: supporting afirst side of a rupture disk blank with a first member having anopening; engaging a second member aligned with the opening in the firstmember with a second side of the rupture disk blank at or near thecenter of the rupture disk blank to displace a section of the rupturedisk blank relative to the first member, thereby creating an indentationat or near the center of the rupture disk blank; and subjecting aportion of the rupture disk blank to a pressurized fluid to form saidportion of the rupture disk blank into a domed shape such that theindentation is disposed at or near the apex of the domed shape.
 22. Themethod of claim 21 , wherein the first member is an anvil and thecenterline of the opening in the anvil is aligned with the center of therupture disk blank.
 23. The method of claim 22 , wherein the secondmember is a punch and the centerline of the punch is offset from thecenter of the rupture disk blank.
 24. The method of claim 21 , whereinthe second member displaces the section of the rupture disk blank inshear.
 25. A rupture disk having an indentation formed in accordancewith the process of claim 21 .
 26. An apparatus for forming a rupturedisk from a blank, comprising: a clamp configured to fixably secure anouter perimeter of the blank, the clamp having a pathway configured todirect a pressurized fluid against the unclamped portion of the blank,the pressurized fluid acting on the unclamped portion to displace theunclamped portion of the blank relative to the clamp; a mold having aconcave shape configured to receive the unclamped portion of the blankas the unclamped portion is displaced relative to the clamp and to formthe unclamped portion of the blank into a domed shape generallycorresponding to the concave shape of the mold; and a member disposed inthe mold and configured to engage the unclamped portion of the blank asthe unclamped portion is displaced relative to the clamp to thereby forman indentation at or near the apex of the domed shape.
 27. The apparatusof claim 26 , wherein the member is a punch and the centerline of thepunch is aligned with the apex of the domed shape.
 28. The apparatus ofclaim 27 , wherein the member is a punch and the punch has a circularcross section.
 29. The apparatus of claim 26 , wherein the member is apunch and the punch includes a tip having a concave surface.
 30. Amethod of forming a rupture disk from a blank, comprising the steps of:clamping the outer perimeter of the blank; directing a pressurized fluidagainst a central portion of the blank to displace the central portionof the blank relative to the outer perimeter and into a mold having aconcave shape; forming the central portion of the blank into a domedshape generally corresponding to the concave shape of the mold; andengaging a member with central portion of the blank as the centralportion is formed into the domed shape to form an indentation at or nearthe apex of the domed shape.
 31. The method of claim 30 , furthercomprising the steps of: removing the member from the mold; anddirecting a pressurized fluid having a second pressure against thecentral portion to reduce the depth of the indentation relative to theapex of the domed shape.
 32. The method of claim 30 , further comprisingthe step of controlling the depth of the indent relative to the apex ofthe dome by adjusting the member relative to the mold.
 33. A rupturedisk formed in accordance with the process of claim 30 .
 34. A rupturedisk assembly to be sealed in a pressurized system, comprising: arupture disk including rupturable portion configured to reverse whenexposed to a fluid having a predetermined pressure, the rupturableportion defining an opening therethrough; and a liner disposed betweenthe rupture disk and the pressurized system, the liner configured tocover and seal the opening in the rupturable portion of the rupturedisk.
 35. The assembly of claim 34 , wherein the rupturable portion hasa domed shape and the opening encompasses the apex of the domed shape.36. The assembly of claim 34 , wherein the liner covers the entirety ofthe rupture disk.
 37. The assembly of claim 34 , wherein the liner isattached to the rupture disk With an adhesive.
 38. The assembly of claim34 , wherein the liner is made from a metallic material and the liner iswelded to the rupture disk.
 39. The assembly of claim 34 , wherein theliner is made of a material that has a greater flexibility than thematerial of the rupture disk.
 40. The assembly of claim 34 , wherein therupturable portion of the rupture disk includes a score line.
 41. Theassembly of claim 34 , wherein the opening is circular.
 42. A rupturedisk to be sealingly engaged with a pressurized system, comprising: anannular flange; and a rupturable portion configured to rupture whenexposed to a fluid having a predetermined pressure, the rupturableportion having a domed shape with a convex surface and a correspondingconcave surface and a structural apex formation disposed at the apex ofthe dome, the structural apex formation including a crease formed in atleast one of the concave and convex surfaces.
 43. The rupture disk ofclaim 42 , wherein the structural apex formation is an indentation. 44.The rupture disk of claim 43 , wherein the indentation is centered atthe apex of the domed shape.
 45. The rupture disk of claim 43 , whereinthe indentation is generally circular.
 46. The rupture disk of claim 42, wherein the crease is in the concave surface.
 47. The rupture disk ofclaim 42 , wherein the crease is generally circular and centered aboutthe apex of the domed shape.
 48. A rupture disk assembly to be sealed ina pressurized system, comprising: a rupture disk having a dome-shapedrupturable portion including a convex surface and a correspondingconcave surface forming a dome area, the rupturable portion including ascore line having a first and a second end, the score line creating aline of weakness along which the rupturable portion will tear when therupturable portion of the rupture disk is exposed to a fluid above apredetermined pressure; and a safety member disposed adjacent theconcave surface of the rupture disk and including a flange and a hinge,the hinge defining first and second pockets configured to receive thearea of the rupturable portion adjacent the respective ends of the scoreline when the rupture disk ruptures.
 49. The rupture disk assembly ofclaim 48 , wherein the hinge extends into the dome area.
 50. The rupturedisk assembly of claim 48 , wherein the hinge lies in the same plane asthe flange of the safety member.
 51. The rupture disk assembly of claim48 , wherein the outer edge of the hinge is generally straight.
 52. Therupture disk assembly of claim 48 , wherein the rupture disk includes aflange and the flange of the safety member is welded to the flange ofthe rupture disk.
 53. The rupture disk assembly of claim 48 , whereinthe safety member includes a stress riser configured to engage therupturable portion of the rupture disk to ensure the rupturable portiontears when the pressure of the pressurized fluid exceeds thepredetermined level.
 54. The rupture disk assembly of claim 53 , whereinthe stress riser includes at least one stress concentrating pointconfigured to contact the score line in the rupturable portion to ensurethe rupturable portion tears along the score line.